| Jiangsu Province is an important area for the production of vegetables in plastic greenhouses in China.The area is located in the middle and lower reaches of the Yangtze River,with large annual rainfall and high groundwater levels.In recent years,water and fertilizer integration technologies based on drip irrigation have been widely used in the region.Similar to other parts of the country,the phenomenon of excessive use of chemical fertilizers in the process of vegetable production in Jiangsu Province is widespread and serious.In this study,a randomized block design with five nitrogen concentration gradients,using the cucumber(Cucumis sativus L.)cultivar Jinchun 5 and tomato(Lycopersicon esculentum Mill.)cultivar Sufen 14 as experimental materials,were carried out to establish critical nitrogen concentration dilution model and nitrogen nutrition index model of these two crops.In addition,different water and nitrogen treatment combinations were performed to investigate the effect of shallow groundwater on the cucumber and tomato yield,WUE(water use efficiency)and NUE(nitrogen use efficiency).We hope the data collected from this experiment could provide useful cues to develop new sensor-based fertigation technology for these two crops in this area.The research results are as follows:1.The relationship between the critical nitrogen concentration of cucumber and tomato and the maximum biomass of aboveground is in line with the power function.In cucumber,it shows%Nc=4.5397DW-0.06,(R2=0.7496,%Nc:critical nitrogen concentration value,DW:Dry matter),the critical nitrogen concentration values of cucumber in 4-leaf stage,first female flower opening stage,first fruiting stage and fruiting stage were 5.35%,5.06%,4.60%and 4.23%respectively;in tomato,it showed%Nc=3.7574DW-0.155,(R-=0.8505),the critical nitrogen concentration values of tomato in the first inflorescence flowering stage,the first inflorescence fruiting stage,the second inflorescence fruiting stage,and the third inflorescence fruiting stage were 4.38%,3.64%,3.09%and 2.60%,respectively.The highest(%Nmax)and lowest(%Nmin)critical nitrogen concentration dilution models of the two crops also have a power function relationship.2.Nitrogen nutrition index model can be obtained from the critical nitrogen concentration dilution curve according to the formula NNI=Nt/Nc(NNI:nitrogen nutrition index,Nt:aboveground nitrogen concentration,Nc:aboveground critical nitrogen concentration).The model can be used to diagnose the nitrogen nutrition status of cucumber and tomato in different growth stages,NNI=1,indicating that nitrogen nutrition is suitable;NNI>1,indicating that nitrogen nutrient is excess;NNI<1,indicating that nitrogen nutrient is deficient.3.Four nitrogen fertilizer gradients 0.5NR,0.75NR,NR and 1.25NR(NR:recommended nitrogen application rate based on traditional fertilization method),4 irrigation amounts 0.5ETc,0.75ETc,ETc and 1.25ETc(ETc:calculated the evapotranspiration of crops)and 2 kinds of irrigation frequency 4d pertime and 2d pertime were performed to study the effects of different combinations of high groundwater level on cucumber yield and WUE and NUE.The results showed that irrigation amount of 75%of estimated ETc was optimal to obtain the highest yield,WUE and NUE,indicating shallow groundwater had a considerable contribution on the cucumber plant evapotranspiration in this condition.75%of the recommended N rate optimize cucumber yield,indicating that drip fertigation helps to improve fertilizer utilization.In high groundwater levels areas,frequent irrigation with low water volume had a beneficial impact on the improvement of cucumber yield,WUE,NUE and reduced the N leaching under the same irrigation amount.4.Three nitrogen fertilizer gradients 0.5NR,0.75NR and NR,4 irrigation treatments-50kPa(irrigation lower limit)to-35kPa(irrigation upper limit);-35kPa to-20kPa;-20kPa to-5kPa and-50kPa to-5kPa based on the soil moisture sensor were performed to study the effects of the above combinations on tomato yield and water and nitrogen use efficiency under high groundwater level.The results showed that irrigation threshold of-35kPa to-20kPa was optimal to obtain the highest yield,WUE and NUE.In this treatment,the total irrigation water amount was far less than the value of estimated ETc,indicating shallow groundwater had a considerable contribution on the tomato plant evapotranspiration and a sensor-based irrigation scheduling might be more suitable than the calculated ETc methods to estimate the water requirement in this condition.75%of the recommended N rate optimize cucumber yield,and excessive nitrogen application results in severe nitrogen leaching or nitrogen overnutrition,indicating that drip irrigation could also improve tomato fertilizer use efficiency. |
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